As various types of mobile electronic devices such as a mobile phone, a personal digital assistant (“PDA”) and a notebook computer are increasingly being developed, the demands for a flat panel display devices which are light, thin, short and small are also increasing. Accordingly, the flat panel display devices, such as a Liquid Crystal Display (“LCD”), a Plasma Display Panel (“PDP”), a Field Emission Display (“FED”), a Vacuum Fluorescent Display (“VFD”) and the like are actively studied. Among them, the LCD device receives a great deal of attention because of its mass-production technique, its facilitation of a driving unit and high picture quality.
The LCD device includes an array substrate on which unit pixels are arranged in a matrix form, a color filter substrate facing the array substrate and displaying color, and a liquid crystal layer filled between the two substrates. The array substrate and the color filter substrate are coupled by a seal line formed at their edge portion and a cell gap is formed therebetween. The cell gap formed entirely through the two substrates is uniformly maintained by spacers.
The spacers may be divided into ball spacers and column spacers. The ball spacers have a fine ball shape, and are formed on the color filter substrate or on the lower array substrate according to a spreading method. The column spacers are formed from a photosensitive organic film by using a photo process. The column spacers are not able to be formed between alignment films of the substrates because of the photo process that is used for creation prevents an alignment layer to be present under and over the column spacers. The alignment layer may be added when the column spacer is in place, so the alignment layer on the column spacer may be next to the alignment layer of one of the substrates.
The ball spacer forming method may be divided into a wet spreading or a dry spreading method. Specifically, the wet spreading method includes mixing spacers in a liquid, such as alcohol, and spreading them. The dry spreading method involves spreading only spacers and includes a static electricity spreading method using static electricity and an antistatic spreading method which uses the spraying pressure of a gas. The antistatic spreading method is largely used for a liquid crystal display panel, which is weak against static electricity.
The formation of ball spacers by using the spreading method is advantageous in that spacers may be easily formed, however the spreading method makes it relatively difficult to form spacers at desired positions and it is difficult to make spreading density uniform. Thus, when spacers are formed according to the spreading method, they may be formed on a pixel region where an image is displayed resulting in degradation of an aperture ratio. Also spreading spacers may gather to cause a defective screen with a possible blot pattern.
The column spacer forming method using the photo process is advantageous in that spacers are formed using a mask designed according to the spacers' formation positions. Accordingly, the spacers' formation positions may be freely controlled and spacers' formation density and form may be also freely controlled. The column spacer forming method has a problem in that it uses the photo process. Specifically, photosensitive films can result in excess waste in order to form spacers, causing an increase in cost and environmental pollution. In addition, since a high-priced mask must be used for the photo process and several additional processes must be performed, the method is not economical.
Thus, instead of the method for forming column spacers by using the photosensitive film and the photo process, a method for forming an appropriate amount of spacers at certain positions by using an ink jet method may be used. The ink jet spraying method for spacers uses a bar type spray nozzle having a plurality of spray holes formed at certain intervals. The spraying nozzle may form a small amount of spacers on a desired position by a dropping method, so the amount of spacers may be reduced compared with the column spacer forming method. In addition, the position for the formation of spacers may be controlled as compared to the ball spacer forming method according to the spreading method.
FIG. 1 is a perspective view showing a method for forming spacers according to a general ink jet spraying method. FIG. 2 shows a section of spacers formed according to the general ink jet spraying method.
As shown in FIG. 1, after an ink jet head 101 is aligned on a color filter substrate 100, spacers 104 are sprayed through a plurality of nozzles formed at the ink jet head 101. The spacers 104 may be formed on the array substrate or on the color filter substrate. Color filter layers 102 are formed in a matrix form on the color filter substrate 100. A black matrix 103 is formed between color filter layers 102 and prevents a light leakage.
The spacers formed by the general ink jet spraying method are sprayed on the black matrix 103, evading the color filter layers 102 defining a pixel region to increase an aperture ratio of the liquid crystal display panel. In addition, for forming spacers according to the ink jet spraying method, solid spherical spacers are put in a volatile solvent and dropped. When the solvent and spacers are dropped, the solvent is volatilized to leave only the spacers. In general, a drop of solvent includes a plurality of spacers. The plurality of spacers are collected and serve as substantial spacers to maintain a cell gap between the upper and lower substrates.
With reference to FIG. 2, the sprayed spacers 201 have a spherical shape. If the size of each spacer is not uniform, the cell gap may differ according to its position. If the spherical spacers 201 formed according to the ink jet method are too large in size, pressure may be generated on the upper substrate 100 or on the lower substrate 105 from the spacers 201. A scratch may be generated on the upper substrate 100 and the lower substrate 105. If the size of the spacers 201 is smaller than the cell gap, the spacers 201 cannot properly support the upper substrate 100 and the lower substrate 105.
FIG. 3A shows an example of a problem that a spherical spacer moves according to an external pressure, and FIG. 3B shows an example in which liquid crystal molecules are erroneously arranged because of the spacer moving according to an external pressure.
With reference to FIG. 3A, when an external pressure is applied to a liquid crystal display panel formed by attaching the upper and lower substrates 100 and 105, the spherical spacers 201 move in directions indicated by arrows from its determined position. In particular, when the spacers 201 are released from the black matrix region due to the pressure applied from outside, liquid crystal molecules arranged around the spacers 201 are disarranged due to the change in the position of the spacers, resulting in a light leakage around the spacers 201.
With reference to FIG. 3B, when an external pressure is applied to the attached liquid crystal display panel, the spherical spacer 201 is changed in its position and the liquid crystal molecules 205b arranged around the spacer 201 become unaligned. Liquid crystal molecules 205a are arranged to have an initial alignment direction. The change in position of the liquid crystal molecules 205b causes a light leakage around the spacer 201 which has been changed in its position.